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c:. Date: January 2, 1996 To: All Interested Persons, Organizations, and Agencies From: Bureau of Reclamation and Southern Nevada Water Authority Administrative Office I 00 I S Valley View Blvd Las Vegas, Nevada 89153 Telephone: (702) 258-3939 Fax: (702) 258-3268 '0 c.. 'r ~- SOUTHERN NEVADA W ATERAUTHORlTf Re: Potential refinements to the Preferred Alternative (SI-1 C) Project Office I850 E. Flamingo, Ste. 234 LdS Vegas, Nevada 89119 Telephone: (702) 732-1982 Fax: (702) 732-2565 As a result of ongoing engineering analysis of the proposed alternatives for the Southern Nevada Water Authority Treatment and Transmission Facility project, refinements to the Preferred Alternative (SI-1C) have been suggested. These refinements include the following options: 1) realigning a portion of the transmission line onto a more direct route to the River Mountains tunnel entry with a transmission tunnel segment on that new alignment, 2) revised siting of the first booster pumping station associated with this realignment, and 31 potential alternative intake pumping station sites on Saddle Island and associated discharge pipeline routes. A more precise definition of the proposed intake location is also suggested. An update to Figure 2.4-1 displaying these new options is attached. A transmission tunnel has been proposed along a segment of the transmission route to the entry of the existing River Mountains Tunnel. The proposed modification would follow the same alignment to the booster pumping station previously described in the Draft Environmental Impact Statement (EIS) for Alternative SI-5. From that location, a tunnel would be constructed along a direct line to connect to the existing River Mountains tunnel entry. A tunnel along this alignment would reduce the amount of land scarring from placement of pipelines and would shorten the overall length of the transmission line. The results of a hydraulic siting constraints analysis support siting of the first booster pumping station between an elevation of approximately 10400 and 1,500 feet. In conjunction with the refinement to the transmission line route in this area described above, the location of the first booster pumping station would be revised to be sited in the general area of an existing Southern Nevada Water System (SNWS) pumping station. Geotechnical borings have revealed poor quality rock at the site for the intake shaft shown on figures in the Draft EIS. Better subsurface rock conditions for an intake have been discovered further south, at a location between the existing SNWS intake and the BMI intake on the eastern side of Saddle Island. This location is within the area described for the intake in the project description of the Draft EIS. Due to the revised intake location, two other options have been suggested for siring of the intake pumping station. A revised intake pumping station site, placed immediately to the south of the existing SNWS intake pumping station, has been suggested. This pumping station could be constructed above ground or below ground. The discharge pipelines associated with this potential intake pumping station site could be routed along one of two routes: 1) a pipeline routed along the western side of Saddle Island which would then cross the causeway as described in the Draft EIS for other alternatives, or 2) a pipeline routed underwater across Boulder Harbor, generally parallel to the existing underwater SNWS pipeline. The Boulder Harbor crossing would be constructed underwater in an open trench. Most of these facility location refinements have been previously analyzed under other alternatives in the Draft EIS or other recent environmental documents. These options are within the immediate project area described in the Draft EIS, and are not considered to be substantially different from the previously described alternatives. A complete analysis of the potential environmental impacts of the selected options will be included in the Final EIS. Please include your comments on these options with your other comments on the Draft EIS, which are due by February 6. 1996. If you require additional time to comment. only for these refinements to the Preferred Alternative, please contact Mr. James P. Green at the address and phone number listed on the enclosed notice and in the Draft EIS. BOARD OF DIRECTORS Eric L. Lundgaard, Vice Chairman Mayor, Boulder City Paul Christemen, Chainnan County Commissioner Jay Bingham Councy Commissioner Arnie Adamsen Las Vegas Councilman Mary Kincaid Nonn Las Vegas Councilman Patricia Mulroy General Manager Robert A. Groesbeck Mayor, Henderson Bruce L. Woodbury County Commissioner